If the battery goes dead,or is replaced the computer in your car looses it's memory and needs to test the emission control system some tests are done immediately some have to meet certain criteria and may take several days or weeks to pass the various drive cycles before the monitors are passed The following is a summary of generic OBD II drive cycle instructions The Intake Air Temperature (IAT) should be between 14 and 122 degrees F. Barometric pressure should be equal to or greater than 75 kPa. The fuel tank should be between 25 and 75% full at the start of the test. During acceleration, keep throttle 1⁄4 to 1⁄2 open. During deceleration, slow to less than 15 mph at an engine speed of less than 1000 rpm without touching the brake or clutch pedal. During cruise, maintain a steady engine speed between 1400 and 4000 rpm. At idle speed, keep the throttle closed and the gear selector in the Neutral position. Remember, these are just the preliminary instructions. The actual drive cycle must conform exactly to the following instructions, or the various monitors may not run to completion. The drive cycle begins with a cold engine startup. The IAT must be between 32 and 85 degrees F. Engine Coolant Temperature (ECT), must be less than 127 degrees F. It may be necessary for the customer to leave the car with you overnight so it can cool down completely. The engine coolant and intake air temperatures must be within a tight range to complete all of the OBD II monitors during the drive cycle. If the IAT input is not between 32 and 86 degrees F at the beginning of the drive cycle, the EVAP monitor will not run. Start the engine and allow it to idle in Park for one to two minutes. Within the first minute and a half, accelerate at 1⁄4 to 3⁄4 throttle to 50-55 mph. Hold that speed for 2-3 minutes. Unless your shop is very close to a major expressway, it may be difficult to satisfy this step in the drive cycle. Decelerate to 0 mph without braking, then idle for 1-2 minutes. If you’re on an expressway, pull safely off the road during this segment. Accelerate to 55 mph, using 1⁄4 to 3⁄4 throttle, then hold a steady cruise for 10 to 20 minutes. Return to 0 mph with the engine idling in Park, then turn the ignition off.

Patricks anwser says it all & more! Drive car to set monitors. Have a knowledgeable shop attatch a scanner and check to see if the monitors set. A 2000 model year car is allowed to have 2 monitors in the incomplete stage.